He came to live with relatives in Stockholm in 1675 at the age of twelve, after having orphaned himself by having his widowed mother Karin Nilsdotter Griis executed, claiming she had abducted him to the sabbath of Satan in Blockula (Blåkulla) where she had molested him sexually.
He told them many stories about the sabbath of Satan, each more fantastic and exciting than the last, and gathered more and more people around him, including adults, and was soon a real celebrity and regarded as an expert on witches and sorcery.
Soon, other children and teenagers, inspired by his stories, began to claim that they had been abducted and taken to Satan too, and the parents in the congregation of Catharina (Katarina) became worried.
After one of these nights, when they thought themselves to have been attacked by the witches, the priest of the congregation gave the mayor a petition signed by the parents, imploring the authorities to investigate to protect their children.
When the Gävle-Boy was questioned, he suddenly changed his testimony; it was not the witch Brita Zippel who had abducted him and the two teenage maids of Myra, Annika and Agnes but himself.
The rest of the accused witches in Stockholm were set free, and the judges decided that the child-witnesses should be whipped and the leading witnesses, the teenaged maids of Myra, should be executed for false testimony.